Global environmental problems such as global warming, ozone layer destruction and the like are coming to the fore. As it has been said that the global warming is significantly affected by CO2 emission, the reduction of CO2 emission, notably the setting of CO2 emission standards, has become a big concern to each country.
One of challenges to reduce CO2 emission is to improve a fuel economy of automotive vehicles, in which lubricating oils play an important role.
As fuel economy improving measures in connection with lubricating oil, the following approaches have been proposed: (1) lowering the viscosity of the lubricating oil, thereby reducing viscous resistance in hydrodynamic lubrication regions and agitation resistance in the engine; and (2) adding an optimum friction modifier and a variety of additives into the lubricating oil so as to reduce a friction loss under the conditions of mixed lubrication and boundary lubrication. Many studies have been made on various friction modifiers including organomolybdenum compounds, such as molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP). As a result of the studies, the lubricating oil containing an organomolybdenum compound which successfully exhibits a low friction coefficient at the early stage of use is applied on a sliding surface formed of a conventional steel material, exhibiting a good effect (See Patent Literature 1).
Patent Literature 1: Japanese Patent Provisional Publication No. 8-20786.